The search results tell you the name of the book in which the keyword phrase appears, the author, and the page on which the phrase appears, if appropriate, or the first page of content for books that contain the keyword phrase in their name.
Click on any results link, and you will see a scanned page from the book with the keyword phrase highlighted. You may be able to browse through more pages, depending on Google's agreement with the publisher. On the right, you'll see more information about the book, book reviews, and links to purchase the book from multiple vendors.
